A wide variety of springs are known. A known spring of the type mentioned in the introduction is a leg spring having two legs and several windings there between which are wound with a constant winding diameter around an axis, adjacent windings being arranged offset relative to each other along the axis by the pitch. The leg spring is tensioned by pivoting the two legs relative to each other about the axis. Accordingly, the built up pretensioning acts in the circumferential direction. Leg springs are especially preferred when the dimension along the axis is to remain constant and the installation space in the radial direction is limited. In order to build up pretensioning in the circumferential direction, it is also possible to use a spiral spring in the case of which all of the windings are laid inside each other in the form of a spiral with a continuously changing winding diameter. Spiral springs are especially preferred when the installation space is greatly limited in the axial direction but is sufficiently available in the radial direction.